Tubular-bowl centrifuges (centrifugal sedimenters) - Pharmaceutical Engineering B. Pharm Third Semester PDF Notes

Tubular-bowl centrifuges (centrifugal sedimenters)

Used to separate solids and liquids when the solid content is low. These consist of a cylindrical 'bowl' 

Around 100 mm in diameter and 1 m long, which rotates at 300-1000 s-1

The product enters at the bottom and centrifugal force causes solids to be deposited on the wall as it passes up the bowl

The liquid overflows from the top

This type of centrifuge can also be used to separate immiscible liquids  

Rate of sediment can be control by controlling the inlet rate

The uses of centrifugal sedimenters include liquid/liquid separation

E.g. During antibiotic manufacture and purification of fish oils, the removal of very small particles, the removal of solids that are Compressible and which easily block the filter medium

The separation of blood plasma from whole blood (need C =3000)

The separation of different particle size fractions, and examining the stability of emulsions

Principle

• Super centrifuge is a sedimentation centrifuge

• The separation is based on the difference in the densities between two immiscible liquids

• Centrifugation is done in the bowl of small centrifuge

• During centrifugation, the heavier liquid is thrown against the wall, while the lighter liquid remains as an inner layer

• The two layers are simultaneously separated using modified weirs

Construction

• It consists of a long hallow cylindrical bowl of small diameter 

• It is suspended from a flexible spindle at the top and guided at the bottom by loose-fit bushing

• It can be rotated on its longitudinal axis

• Provision is made at the bottom for the feed inlet using pressure system 

• The liquid outlets are provided at different heights at the top of the bowl, and modified weirs, are attached